The Internet search engine has become an important source of revenue for the service providers who operate them. The revenue is primarily generated from the display of advertisements to search engine users. The more Internet traffic that a search engine receives, the more attractive it is to advertisers, and the more revenue it can generate. It is generally regarded that the best way search engines can increase traffic is to provide highly relevant search results. But what is relevant today may not be relevant tomorrow, or even relevant later the same day. It is difficult for service providers to keep pace with the rapid changes in searchable content based on seasonal and popular trends and topical events in the news.
Complicating matters is the increasingly popular use of paid advertisements directly in the list of results that the search engine generates. The advertiser bids on popular search terms in exchange for which the search engine prominently lists their advertisement along with the other unpaid search results returned for the bidded search term. For example, when a user types in the search term “digital camera,” the search results list might include a paid listing for Nikon® brand digital cameras preceding a relevant but unpaid listing for an independent digital photography Web site that reviews several brands of digital cameras.
The practice of including paid listings along with the search results is commonly referred to as pay-per-click advertising, since the advertiser pays only when the user actually clicks on the listing (as opposed to more conventional Internet advertising, referred to as pay-per-impression, where the advertiser pays whenever the listing is displayed). Pay-per-click advertising is somewhat at odds with providing highly relevant search results, as the user might not consider the paid listings to be particularly relevant to their search. Cluttering up the search results with pay-per-click (PPC) listings in which users show little interest may impair the user experience to such an extent that traffic to the search engine site declines as users choose to conduct their Web searches elsewhere. Moreover, low-performing PPC listings, i.e., those with a low click-through rate, generate little revenue, regardless of how much the advertiser might have bid for the search term. Thus, the small revenue gained from low-performing listings may not be worth the risk of alienating users by displaying them along with the more relevant but unpaid search results.
Since the amount of display area in a search results page is limited, some search engine operators place potentially less relevant search results as well as PPC listings for some or all bidded search terms off to one side-referred to as the sidebar-instead of placing them directly in line with the relevant unpaid listings. For instance, during the Thanksgiving season, the search term “turkey” might produce seasonal “in-line” listings for Thanksgiving turkey preparation (either unpaid or PPC listings) that would normally be placed in the sidebar with the twin goals of (a) increasing revenue for the search engine, and (b) increasing relevance of the results for the user. Search engine operators might also place potentially lower revenue paid listings for bidded search terms in the sidebar as well. Using the digital camera example, the search results list might include a PPC listing for competing Sony® brand digital cameras placed in the sidebar next to the in-line listings for Nikon and the independent digital photography Web site, because the amount of Sony's bid for the search term “digital camera” was less than Nikon's.
In addition to maximizing the use of the available display area, sidebar placements have the advantage of being less distracting to the search engine user. However, experience has shown that the click-through rate for sidebar placements is inherently lower than the click-through rate for in-line placements, regardless of a particular listing's click-through performance. Not surprisingly, users are simply less likely to notice and click listings appearing in a less desirable sidebar location than those appearing in the more desirable in-line location, i.e., directly in the list of search results. Consequently, one of the problems with placing listings in the sidebar is that such placements will likely generate less revenue and attract less repeat traffic than their in-line counterparts, even when the listings are otherwise high performers. Furthermore, as noted already, what is relevant today may not be relevant tomorrow, or even relevant later the same day. The determination of where to best place search result listings can change rapidly, making it difficult to place listings in the optimal location at any given time.